The present invention relates to filter stacks. Filter stacks are used in many different types of air purifying equipment, from large commercial air purifiers for industry, to small compact room air conditioners.
A filter stack comprises a plurality of frames, each having openings along one edge, clamped together with a filter element between adjacent frames. The frames are alternately arranged with the openings in one frame opening in a first direction and the openings in the alternate frames opening in the opposite direction. In this way, air is drawn through one set of openings in the first set of frames, through the filter elements and then out through the openings in the second set of frames.
The small openings in the edges of the frames do cause restricted air flow. If one makes the frames wider, one can increase the size of the edge openings. However, one increases the volume of the stack with the same number of filter elements, thus decreasing the filter effectiveness per unit of volume.
Keeping the filter stack together so as to prevent air from leaking between adjacent frames is also difficult. Some artisans clamp the frames together with long bolts which extend completely through all of the frames of the stack. There is a tendency for the frames to bow apart in areas not directly adjacent the clamping bolts.
Another problem is that the filter elements can become misaligned between adjacent frames. This causes small gaps around the edges of the filter which can allow air to leak through the system without being filtered.